1. Field of the Invention
The present invention relates to a control valve device for a hydraulic elevator, and more particularly to a control valve device for a hydraulic elevator capable of controlling an RPM of a hydraulic pump and thereby controlling the delivery of a pressurized fluid to a hydraulic cylinder or the quantity of a pressurized fluid discharged out of the hydraulic cylinder.
2. Description of the Prior Art
FIG. 1 is a circuit diagram illustrating a conventional control valve device for a hydraulic elevator. In FIG. 1, the reference numeral 1 denotes a car for carrying passengers, while the reference numeral 2 denotes a main rope fixedly mounted at one end thereof to the ground and connected at the other end thereof to the car 1. The main rope 2 extends between the ground and the car 1 via a pulley 3 coupled to the upper end of a ram 4a upward spaced a certain distance apart from the ground. The ram 4a is received in a hydraulic cylinder 4. To the hydraulic cylinder 4, a hydraulic hose 5 is connected at one end thereof. The other end of the hydraulic hose 5 is connected to a pilot operating main check valve 6.
On the other hand, a pressure detecting unit 21 is provided between the hydraulic cylinder 4 and the main check valve 6 to detect a pressure in side of the hydraulic cylinder 4.
The main check valve 6 is connected at one end thereof to a pilot line 10. On the pilot line 10, an opening solenoid valve 8 and a closing solenoid valve 9 are positioned and spaced an appropriate distance apart from each other. The closing solenoid valve 9 is connected to an oil tank 20 which is disposed beneath the closing solenoid valve 9.
To the main check valve 6, a normal/reverse rotation hydraulic pump-side pressure detecting unit 22 is connected so as to detect the pressure of a normal/reverse rotation hydraulic pump 17. A pilot operating unload relief valve 12 is connected to the hydraulic pump-side pressure detecting unit 22. The pilot operating unloading relief valve 12 serves as a safety valve and operates to obtain a required pressure. Connected to the pilot operating unloading relief valve 12 is a throttle valve 11, to which an unloading solenoid valve 14 is connected. A relief valve 13 is also connected to the pilot operating unloading relief valve 12.
At the downstream of the relief valve 13 and the solenoid valve 14, a check valve 15 is disposed which serves to allow a pressurized oil emerging from each of the relief valve 13 and the solenoid valve 14 to flow only in one direction. The check valve 15 prevents the pressurized oil from flowing the other direction.
On the other hand, a three-phase induction motor (variable motor) 19 is connected to the normal/reverse rotation hydraulic pump 17. An oil filter 18 is connected to the normal/reverse rotation hydraulic pump 17. The oil filter 18 serves to filter an oil (operating fluid) emerging from the normal/reverse rotation hydraulic pump 17. The oil tank 20 receives the filtered oil from the filter 18 and stores it therein.
To the three-phase induction motor 19, an inverter 24 is connected. The inverter 24 is also connected to a speed control unit 23. The speed control unit 23 is coupled to the pressure detecting unit 21 in side of the hydraulic cylinder 4 and to the pressure detecting unit 22 in side of the hydraulic pump 17 so that it receives a pressure signal detected by the pressure detecting unit 21 and a pressure signal detected by the pressure detecting unit 22 respectively via output signal transmission lines 21a and 22a.
Operation of the conventional control valve device having the above-mentioned arrangement will now be described.
When an ascending operation command for the car 1 is generated by an operator, the cylinder-side pressure detecting unit (for example, a pressure sensor) 21 performs its detecting operation to detect a cylinder-side pressure and generates a signal indicative of the detected pressure. The pressure signal from the cylinder-side pressure detecting unit 21 is sent to the speed control unit 23 via the output signal transmission line 21a. Simultaneously, the pump-side pressure detecting unit 22 performs its detecting operation to detect a pump-side pressure and generates a signal indicative of the detected pressure. The pressure signal from the pump-side pressure detecting unit 22 is also sent to the speed control unit 23 via the output signal transmission line 22a. The pressure detected in side of the hydraulic cylinder 4 is determined as a reference pressure. After completing the detection of the reference pressure, the speed control unit 23 generates a motor drive signal using the pressure signal from the pump-side pressure detecting unit 22 as a feedback signal, so as to make the delivery pressure of the hydraulic pump 17 to correspond to the reference pressure. The motor drive signal from the speed control unit 23 is applied to the inverter 24 which, in turn, generates a three-phase variable AC voltage of a variable frequency corresponding to the drive signal. The AC voltage is applied to the three-phase induction motor 19, thereby enabling the three-phase induction motor 19 to be driven. By the drive force of the three-phase induction motor 19, the hydraulic pump 17 operatively connected to the induction motor 19 rotates normally, so that it increases in delivery pressure. When the delivery pressure of the hydraulic pump 17 detected by the pump-side pressure detecting unit 22 reaches the reference pressure, the speed control unit 23 generates a speed command corresponding to the speed command for the car 1 so as to control the rotation speed of the induction motor 19. As the rotation speed of the induction motor 19 increases, the delivery oil quantity of the hydraulic pump 17 increases, so that the pressurized oil emerging from the hydraulic pump 17 can rise while pushing the pilot operating main check valve 6. The pressurized oil passing through the check valve 6 is fed to the hydraulic cylinder 4 via the hydraulic hose 5, thereby causing the car 1 to move upward. When the car 1 approaches to a desired stop floor, the rotation speed of the induction motor 19 is decreased until the delivery oil quantity of the hydraulic pump 17 is zero. Under this condition, the hydraulic cylinder 4 discharges the pressurized oil no longer because the main check valve 6 serves as a general check valve. As a result, the car 1 is stopped.
On the other hand, where a descending operation command for the car 1 is generated by the operator, the normal rotation of the induction motor 19 is achieved in the same manner as in the ascending operation. In this case, the opening solenoid valve 8 is switched to its ON state when the delivery pressure of the hydraulic pump 17 corresponds to the pressure in side of the hydraulic cylinder 4. At this time, the closing solenoid valve 9 is also switched to its ON state. Under this condition, the pressure always generated in the hydraulic cylinder 4 by the weight of the car 1 is applied to an oil quantity control chamber 7 defined in the main check valve 6 via the pilot pipe 10. That is, the pressurized oil from the hydraulic cylinder 4 is fed to the oil quantity control chamber 7, thereby causing the main check valve 6 to shift to its left position. At the left position of the main check valve 6, the pressurized oil from the hydraulic cylinder 4 flows to the hydraulic pump 17 in accordance with the speed command for the car 1. As a result, the car 1 can move downward. During the downward movement of the car 1, the rotation of the hydraulic pump 17 is braked by the induction motor 19 to control the delivery oil quantity of the hydraulic cylinder 4.
When the car 1 approaches to a desired stop floor, the rotation speed of the induction motor 19 is decreased so as to decrease the delivery oil quantity of the hydraulic cylinder 4. When the car 1 reaches the stop floor, the opening solenoid valve 8 is switched to its OFF state. At the OFF state of the opening solenoid valve 8, the pressurized oil from the oil quantity control chamber 7 of the main check valve 6 is discharged to the oil tank 20. The closing solenoid valve 9 is also switched to its OFF state, thereby causing the main check valve 6 to be switched to a state that it performs a complete check valve function.
Meanwhile, when the delivery pressure of the hydraulic pump 17 is higher than a predetermined pressure of the pilot operating unloading relief valve 12, the pressurized oil emerging from the hydraulic pump 17 passes through the relief valve 12. As a result, the pressurized oil is stored in the oil tank 20 after passing through a conduit 16 connected to the oil tank 20.
When the temperature of the operating oil is lower than a temperature in a rated use of the operating oil, the unloading solenoid valve 14 is switched to its ON state. At the ON state of the unloading solenoid valve 14, the operating oil, that is, the pressurized oil is allowed to pass through the relief valve 12, so that the temperature of the pressurized oil is increased. Where the opening solenoid valve 8 does not operate even though it is applied with an operating signal upon descending the car 1, a cavitation may occur due to a negative pressure generated upon a reverse rotation of the hydraulic pump 17. In order to avoid such a cavitation, the relief check valve 15 is opened in response to the generation of negative pressure so that the operating oil from the oil tank 20 can be supplied to the hydraulic pump 17.
Since a pilot pressure from the hydraulic cylinder 4 is applied to the main check valve 6 via a pilot line 10, the main check valve 6 is maintained at a forcedly opened state, if the opening solenoid valve 8 is maintained at its ON state due to its abnormal operation. In the conventional hydraulic elevator, accordingly, the car 1 may have a danger of a continued descent of the car 1. When the viscosity of the pressurized oil is degraded due to an increase in temperature of the pressurized oil, a spool of the main check valve 6 may not perform the complete check valve function, thereby causing an internal leakage to occur in the main check valve 6. As a result, an undesirable descent of the car 1 may occur. In other words, the main check valve 6 may not perform its check valve function upon a variation in viscosity of the pressurized oil. Furthermore, the conventional control valve device has no valve for manually descending the car 1 in an emergency. For manually descending the car 1 in the conventional case, the pilot operating main check valve 6 should be used. This use of the main check valve 6 is dangerous.